Model trains have had a long and illustrious history. From the earliest model trains to the present, one of the primary goals of model train system designers has been to make the model train experience as realistic as possible for the user.
The typical model train has an electric motor inside the train that operates from a voltage source. The voltage is sent down the model tracks where it is picked up by the train's wheels and rollers, then transferred to the motor. A power source supplies the power to the tracks. The power source can control both the amount (amplitude) and polarity (direction) of the voltage, so that the user may control both the speed and direction of the train. Some systems use a DC voltage applied to the track. In others, the voltage is an AC voltage, and is usually the 60 Hz AC voltage available from standard U.S. wall outlets. In these systems, a transformer is necessary to reduce the amount of voltage provided to the system.
Using the above-described system, an early method of operating model trains is now referred to as “legacy” mode. As the user increases or decreases the amount of voltage applied to the track through manipulation of a throttle on the power source, the train will gain or lose speed as it travels along the track. This is a straightforward operation whereby the user directly controls the amount of voltage applied to the train's motor. Such a mode of operation requires the user to constantly monitor and adjust the amount of voltage applied to the tracks. For example, a train approaching a curve in the track may de-rail if the train is moving too fast. The user must therefore reduce the amount of voltage received by the train's motor by cutting back on the power source throttle prior to the train reaching the curve. Similar situations may occur elsewhere on the track layout, such as when the train approaches an upgrade (which may require the user to increase the amount of voltage applied) or when the train is attached to a heavy load.
In addition to being able to control the speed and direction of model trains, early train systems enabled the user to operate a whistle (or horn) and later a bell located on the train. In AC-powered systems, this was done by applying a DC offset voltage superimposed on the AC voltage applied to the track. In later systems, the train had circuitry that distinguished between the polarities of the DC offset voltage. Thus, for example, the whistle (or horn) would blow when a +DC offset voltage was applied to the track, and the bell would ring when a −DC offset voltage was applied. Typically, the user would press a “horn” or “bell” button located on the power source to effect the desired sound.
It should be apparent that the above-described system provided the user with only limited control over the operation of the train, and further required constant manual manipulation of the power source in order to maintain the train on the track layout. Later-developed systems therefore attempted to address these shortcomings and thereby increase the realism of the model train experience.
Two examples of such systems include those disclosed in U.S. Pat. No. 5,251,856 to Young et al., and Marklin's Digital line of model trains. These systems enabled the user to have remote control operation of the train. This was accomplished by inserting a control unit between the power source and the tracks. The control unit responded to commands entered by the user on a hand-held remote control. These types of systems generally utilized microprocessor technology. A microprocessor or receiver located in the model trains would have a unique digital address associated with it. The user would enter the train's address and a command for the train on the remote control, such as “stop,” “blow whistle,” “change direction,” and so on. The address and commands would be implemented as infra-red (IR) or radio frequency (RF) signals. The control unit would receive the commands and pass the commands through the tracks in digital form, where the model train corresponding to the entered address would pick up the command. The microprocessor inside the model train would then execute the entered command. For example, if the user had entered a command such as “turn on train light,” the microprocessor would send a signal to the light driver circuit located inside the train, and the light driver circuit would turn on the light.
In the aforementioned U.S. Pat. No. 5,251,856, the user is able to control the speed of the train through the remote control. This is accomplished through the use of a triac switch located inside the control unit. The power source is set to a maximum desired level. In response to input from the user, the triac switch inside the control unit switches the AC waveform from the power source at appropriate times to control the AC power level and impose a DC offset. The speed of the trains will then change in accordance with the change in power applied to the track. The aforementioned Marklin system, on the other hand, controls the speed of the trains by use of pulse width modulation (PWM) and fullwave rectifier circuits located inside the train. The duty factor of the output signal from the PWM circuit varies between 0 and 15/16 at a frequency that is 1/16 of a counter frequency that remains constant. This allows the user a 16-step speed control for each train.
Many other advances have been made in model trains beyond those described here. For example, U.S. Pat. No. 4,914,431 to Severson et al. describes the use of a state machine in the train that increases the number of control signals available to the user for control over train features such as sound volume, couplers, directional state, and various sound features. U.S. Pat. No. 5,448,142 discloses, among other things, ways to improve the quality and realism of sounds made by the train during operation. Still, further advances in the area of model trains are desirable, in order to approach the desired goal of realism during operation.